Hydrocarbon feedstocks such as petroleum crudes, gas oil, etc. are subjected to various processes in order to isolate and separate different fractions of the feedstock. In refinery processes, the feedstock is distilled so as to provide light hydrocarbons, gasoline, naptha, kerosene, gas oil, etc.
The lower boiling fractions are recovered as an overhead fraction from the distillation zones. The intermediate components are recovered as side cuts from the distillation zones. The fractions are cooled, condensed, and sent to collecting equipment. No matter what type of petroleum feedstock is used as the charge, the distillation equipment is subjected to the corrosive activity of acids such as H.sub.2 S, HCl, and H.sub.2 CO.sub.3.
Corrosive attack on the metals normally used in the low temperature sections of a refinery process system, i.e. (where water is present below its dew point) is an electrochemical reaction generally in the form of acid attack on active metals in accordance with the following equations:
(1) at the anode: PA1 (2) at the cathode:
Fe.revreaction.Fe.sup.++ +2(e) PA2 2H.sup.+ +2(e).revreaction.2H PA2 2H.revreaction.H.sub.2
The aqueous phase may be water entrained in the hydrocarbons being processed and/or water added to the process for such purposes as steam stripping. Acidity of the condensed water is due to dissolved acids in the condensate, principally HCl and H.sub.2 S and sometimes H.sub.2 CO.sub.3. HCl, the most troublesome corrosive material, is formed by hydrolysis of calcium and magnesium chlorides originally present in the brines produced concomitantly with the hydrocarbons, oil, gas, condensates.
Corrosion may occur on the metal surfaces of fractionating towers such as crude towers, trays within the towers, heat exchangers, etc. The most troublesome locations for corrosion are the overhead of the distillation equipment which includes tower top trays, overhead lines, condensers, and top pump around exchangers. It is usually within these areas that water condensation is formed or is carried along with the process stream. The top temperature of the fractionating column is maintained about at or above the boiling point of water. The condensate formed after the vapor leaves the column contains significant concentration of the acidic components above-mentioned. This high concentration of acidic components renders the pH of the condensate highly acidic and, of course, dangerously corrosive. Accordingly, neutralizing treatments have been used to render the pH of the condensate more alkaline to thereby minimize acid-based corrosive attack at those apparatus regions with which this condensate is in contact.
Prior art neutralizing agents include ammonia, morpholine, cyclohexylamine, diethylaminoethanol, monoethanolamine, ethylenediamine and others. U.S. Pat. No. 4,062,764 (White et al) suggests that alkoxylated amines, specifically methoxypropylamine, may be used to neutralize the initial condensate. U.S. Pat. No. 3,779,905 (Stedman) teaches that HCl corrosion may be minimized by injecting, into the reflux line of the condensing equipment, an amine containing at least seven carbon atoms. Other U.S. patents which may be of interest include U.S. Pat. Nos. 2,614,980 (Lytle); 2,715,605 (Goerner); and 2,938,851 (Stedman).
The use of such prior art neutralizing agents has not been without problem, however, For instance, in many cases the hydrochloride salts of neutralizing amines form deposits in the equipment which may result in the system being shut down completely for cleaning purposes. Also, as the use of sour crudes has increased, in many cases the neutralizing agent has demonstrated an affinity to form the sulfide salt, thus leaving the more corrosive HCl, unreacted in the condensate and causing severe corrosion.
Accordingly, there is a need in the art for a neutralizing agent which can effectively neutralize the condensate in refinery systems without resulting in excessive system fouling. There is a further need for such a neutralizing treatment which can function effectively in those systems charged with a high sulfur content feedstock.